My local (US) grocery story has a similar scan-as-you-go feature available, and I haven't seen a single person using it in the year or so that it has been available. For older folks and the tech-illiterate, it is likely somewhat intimidating to have to teach yourself a new 'techie' feature on the fly.

Amazon's method may require you to log in or scan in with a barcode from the Amazon app, but just about everyone already has some basic experience with the Amazon service. And once you do a single scan, it just works.